We will study aspects of male pronuclear chromatin structure and composition in the sea urchin. The histone composition during the first cycle of polyspermically fertilized eggs will be analyzed by 2-dimensional polyacrylamide gel electrophoresis and peptide mapping. The structure of the chromatin will be analyzed by micrococcal nuclease digestion (to determine nucleosomal repeat lengths) and chemical crosslinking with Lomant's Reagent (to distinguish neighboring variants within individual nucleosomes). Secondary modifications of histone variants, particularly phosphorylations will be analyzed through the cell cycle. In vitro assembly of chromatin from stored cleavage stage histone variants and exogenously added closed circular DNA will be performed and this chromatin compared with in vivo forms.